1. Field of the Invention
This invention relates to photographic processing apparatus and particularly to apparatus for controlling the composition and addition rate of replenishment solutions used in photographic processing apparatus.
2. Description of the Prior Art
It is well known in the art of developing silver halide photographic films in automatic processing apparatus the developer solutions are subject to change due to accumulation of development products and aerial oxidation. To obtain reproducible, automatic processing, a replenisher solution is normally added to compensate for the changed activity of the developer solution due to prior use or aging. Such addition can be accomplished manually by the operator based on visual observations of processed sample strips. On the other hand automatic equipment can be used to either chemically analyze the processing solutions or read the density of processed strips and feed back the data to metering means to replenish the solutions.
When the addition of replenishing solution is done manually, even with the aid of charts to assist the operator in determining the appropriate amounts to be added, the system is subject to operator error. As the number of variables that must be taken into consideration increase, the estimation of the amount and rate of replenishment becomes exceedingly complex. A number of semi-automatic processors are available allowing a limited, preselected choice of replenisher addition based on the film size, degree of exposure and type of film used. However, such corrections do not compensate for oxidation of the processing solution due to aging. Such oxidation is dependent upon the history of the processing solution in the processor, and correct compensation can only be achieved by accounting for every piece of processed material that has gone through the equipment, the corresponding replenisher addition, the rate of oxidation in the tank, and the time that has elapsed since the last addition.
When the addition of replenishment is controlled by automatically sampling the processing solutions, such problems are minimized but the complexity and cost of equipment greatly increase, while reliability suffers.
Schumacher, U.S. Pat. No. 3,529,529 discloses a method and apparatus for the addition of replenishment solution to compensate for changed activity by sampling and titrating developer bath.
Freidel, U.S. Pat. No. 3,334,566, discloses a photographic developing apparatus using sensing means and a variable impulse control for maintaining the concentration of developer solution by addition of processing chemical solutions.
Frutiger, U.S. Pat. No. 3,561,344 discloses an apparatus for processing photographic film in which replenisher, developer and fixer solutions are supplied on demand. The continuously moving, fixed photographic film is light monitored to provide a plurality of modulated signals which are a function of the degree of transparency presented by the photographic film being processed.